1. Field of the Invention
The present invention relates to a mobile wireless terminal having an antenna device extensible from the case of the mobile wireless terminal and, more particularly, to an improvement for preventing the antenna performance from deterioration.
2. Description of the Prior Art
A mobile wireless terminal capable of mobile communication is usually susceptible to wide fluctuations of the situation of electromagnetic waves during transit, and requires stable antenna performance in order to ensure stable wireless characteristics. Especially in communication taking place close to a human body, as the antenna is very close to the human head which is apt to inflict loss, the antenna performance may be greatly deteriorated by the human head, and in a state in which the antenna is stowed, the antenna is closer to the human head than when it is extended, and accordingly its performance is even more susceptible to deterioration by the head.
Furthermore, as the angle formed by the case of the mobile wireless terminal and the human head varies during communication, the antenna sometimes approaches and at other times moves away from the human head with a destabilizing effect on the antenna performance.
FIG. 1 and FIG. 2 show front views of a mobile wireless terminal according to the prior art in some of the ways it is used during a call. In the drawings, the conventional mobile wireless terminal is provided with an upper case 100 having a receiver section 104 and a lower case 101, and the two cases are rotatably connected by a hinge section 103. The upper case 100 accommodates an extensible antenna, which can be drawn out of the case, and its tip section 105 projects from the upper end of the upper case 100. The antenna tip section 105 has an antenna coil section inside. A tangent 120 in FIG. 1 and FIG. 2 is the tangent of contact between the upper case 100 of the mobile wireless terminal and a human face (cheek), and a line 121 is the central axis of the antenna.
According to the prior art, when the inner face (the face that is inside when the terminal is folded) of the upper case 100 is in contact with the user's cheek as shown in FIG. 1, the antenna tip section 105 is at a distance B from the human head.
However, when the case is rotated round the upper end 106 of the upper case 100 on the side in contact with the cheek and the inner face of the upper case 100 moves away from the cheek as shown in FIG. 2, the distance (D<B) between the antenna tip section 105 and the human head varies in the direction of bringing the cheek closer to the tip section of the antenna, resulting in substantial variations in the impedance characteristic and the radiation characteristic of the antenna.